Injection valves are used where an operator wishes to inject a fluid into a pressurized downhole environment. The fluid may, for example, be water or gas which is to be injected into the formation to maintain reservoir pressure.
Some conventional injection valves comprise a plug biased by a spring to a position in which the valve outlet is sealed closed. To inject fluid through the valve, the fluid is pressurized against the plug until there is sufficient fluid pressure to overcome the closing force of the spring, permitting the valve to open.
There are disadvantages associated with this type of arrangement. For example, when the fluid pressure has built up sufficiently to overcome the spring closing force, and the plug moves to open the outlet, there is an immediate release of pressure as fluid flows through the valve. In this situation the fluid pressure can drop sufficiently to permit the valve to close under the action of the spring. The pressure then builds up behind the plug and an oscillation cycle of valve opening and closing can be established. This oscillation cycle causes vibration in the string and can lead to damage of the sealing interface between the plug and the valve housing. Additionally, as the plug is opened, and the pressurized fluid passes between the plug and the housing, the movement of the fluid can erode the valve and the surrounding components such as the bore casing or tubing.
It is an object of the present invention to obviate or mitigate at least one of the aforementioned disadvantages.